Producing brittle titanium metal



Oct. 24, 1961 c. TAO

PRODUCING BRITTLE TITANIUM METAL Filed April 9. 1959 INVENTOR Luh C. Too

11.; Agent United States Patent Ofiice 3,005,698 Patented Oct. 24, 196i 3,005,698 PRQDUCHNG BRITTLE TETA NETAL Lula C. Tao, Lincoln, Nehru, assignor to Titanium Metals Corporation of America, New York, N.Y., a corporation of Delaware Filed Apr. 9, 15 59, Ser. No. 805,346 6 Claims. (Cl. 75-.'5)

This invention relates to the production of a hydrogenated titanium alloy product and more particularly to a brittle hydrogenated titanium alloy product which may be readily crushed or subdivided without production of more than a minor percentage of fine particles.

It is known that titanium and titanium metal alloys will become hard and brittle when hydrogenated. Therefore, a hydrogenation process has been proposed to increase brittleness of such materials so that they may be readily crushed to provide subdivided products. Such hydrogenation processes applied particularly to strong and ductile alloys have often heretofore produced a prodnot which is brittle to the extent of being crumbly, or, if not sufiiciently hydrogenated, substantially impossible to crush. When crumbly material is subdivided in conventional crushing equipment, an undesirably high percentage of fine particles has been produced and often the resulting product is essentially fine powder. Efforts to reduce the production of fines by limiting the amount of hydrogenation has resulted in poor crushability in the resulting hydrogenated material.

it is therefore an object of this invention to provide an improved process for subdividing titanium alloy pieces. Another object of this invention is to provide a hydrogenated titanium alloy product of improved frangibility which may be readily crushed without production of an excess proportion of fine particles. A further object of this invention is to provide a process for improving the frangibility of hydrogenated titanium alloy product. These and other objects of this invention Will be apparent from the following description thereof; and from the accompanying drawing which illustrates the structure of the product produced by the process of this invention, and in which:

The figure shows at a magnification of 2,50 diameters the formation of titanium hydride crystals in clusters which are distributed in the product of this invention.

This invention in its broadest aspects contemplates producing a brittle hydrogenated titanium alloy product by treating pieces of such titanium alloy in a closed container which is provided with an atmosphere of hydrogen maintained at super atmospheric pressure and at a temperature between about 600 C. and about 875 C. until the hydrogen content thereof is between 0.5% and 2% by weight. The hydrogenated alloy is then heated at a temperature between 825 C. and 875 C. for a period of time not less than about 15 minutes and subsequently cooled at a rate not exceeding 2 C. per minute to a temperature below 800 C. and preferably below about 650 C. Subsequently the alloy may be cooled at faster rate to room temperature. After cooling the alloy is crushed to produce a subdivided product composed of a majority of unitary small fragments and a minor amount of powdery fines.

Titanium alloys to which the process of this invention is applicable are of the alpha beta of all beta type. These alloys contain so-called beta stabilizer alloying elements which promote retention of beta phase titanium at room temperature. Such beta stabilizing elements include among others, vanadium, molybdenum, chromiun, iron, manganese, columbium and tantalum. A large proportion of such elements, often more than 10% to Will produce an all beta alloy, whereas smaller proportions, and inclusion of effective amounts of alpha stabilizers such as aluminum, tin and to a degree zirconium, will result in alloys at room temperature containing both alpha and beta phase titanium and designated as alphabeta type mloys. Examples of alpha-beta and all beta alloys are Ti-6% Al-4% V, Ti-2% Cr-2% Mo-2% Fe, Ti-4% Al-4% Mn, Ti5% Fe5% C1'-4% Mo, Ti-11% Cr-13% V-3% Al.

Hydrogenation of the titanium alloy pieces is accomplished by heating under a hydrogen atmosphere in a closed container. A temperature between about 600 C. and about 875 C. may be employed, but it will generally be found that hydrogen absorption by the metal will be somewhat greater in the temperature range between 600 C. and 750 C. In operation the pieces or chunks to be hydrogenated are placed in a closed container which is then sealed and evacuated. The'temperature of the metal in the container is raised to about 600 C. to 650 C. and the container back filled with hydrogen gas. The hydrogen gas pressure is maintained at a pound or so and preferably not more than 10 pounds pressure above atmospheric with the temperature maintained preferably between about 650 C. to 750 C. until more than 0.5 and up to about 2% hydrogen has been absorbed by the titanium alloy. The amount of hydrogen absorbed during processing may readily be calculated from considerations of the temperature, hydrogen pressure and volume values, time, and the weight of alloy in the container.

At the end of the hydrogenation step the alloy pieces are heated and maintained at a temperature from about 825 C. to 875 C. for at least 15 minutes and, subsequently cooled slowly to a temperature below 800 C. Heating at temperatures below about 825 C. will not provide the desired effect and temperatures above about 875 C. are not desirable because of limitations of container materials of construction. More than 15 minutes heating time could be employed but it will be found that extension of this time beyond about 30 minutes will produce no additional benefit and is wasteful of time, labor, and processing costs. Cooling from the heating temperature must be slow, that is, not faster than 2 0. per minute and preferably not faster than 1 C. per minute. An advantageous cycle comprises heating to a temperature of about 850 C. and maintaining at this temperature for twenty minutes and then gradually cooling to a temperature of about 650 C. in a period of 3 hours. At

this point the material may be cooled at a faster convenient rate to room temperature, if desired.

It is immaterial that the heating step be distinctly separate from, or a part of, the end of the hydrogenation step. Thus the heating 'at 825 C. to 875 C. may occur at the final stage of hydrogenation or may be accomplished separately. It is necessary that the heating and subsequent slow cooling be conducted in a non-contaminating atmosphere. Therefore it may be convenient to carry out this processing under hydrogen, which, of course, may result in additional, though probably incidental, hydrogenation, or if desired the hydrogen atmosphere may be replaced by an inert gas such as helium or argon.

Crushing of the hydrogenated, heated and cooled alloy is carried out in a suitable crushing machine, preferably an imp-act mill or jaw crusher. The action of such mill may be adjusted, as will be apparent to those skilled in the art, to produce a subdivided product of required average or maximum particle size. The crushed product is useful for metallurgical or chemical purposes requiring such metal in subdivided form. It may, if desired, be dehydrogenate-d and may be employed as part or all of feed for remelting into ingots for further fabrication. Employment of hydrogenated scrap of titanium or titanium base alloys in consumable electrodes for remelting without intermediate dehydrogenation is more particularly de- V r 3 scribed and claimed in co-pending application SerialNo. 800,954, filed March 23, 19 59, now Patent No. 2,992,094.

Reference to the figure will show the unique microstructure which results from the heating and cooling process described herein. The figure shows a typical section of a piece of titanium base alloy containing 6% aluminum, 4% vanadium and 1.4% hydrogen heated and cooled according to this invention and photographed at a magnification of 250 diameters. The alloy matrix background is designated at 1, and the titanium hydride in the form ot'clustersof crystals as at 2. The clustering or agglomeration of titanium hydride crystals is the result of the heating and cooling process, since as originally .formed and as in heretofore produced hydrogenated titanium products, the compound titanium hydride is present as a finely and uniformly dispersed hydride phase. It is not known precisely why the clustering of crystals occurs under the described conditions but it is known that titanium hydride is more soluble in beta than alpha phase titanium, and this may account for the results obtained employing alpha-beta and beta type titanium alloys. The hydride clusters evidently produce discontinuities, or planes, or areas of weakness in the over all structure and result in substantially enhanced frangibility compared to metal containing titanium hydride in uniformly dispersed state. The heated and cooled product is frangible in that it may be readily broken or crushed and in such breaking or crushing will not tend to form a large percentage of fine particles.

The following illustrates an example of the practice of an embodiment of the process of this invention.

Example 1 A charge of 6% Al-4% V titanium alloy rods of random lengths and'diameter up to about one inch was hydrogenated in a closed container at a temperature of about 750 C. employing a hydrogen pressure of up to one pound gauge until a hydrogen content of 1.4% in the metal was obtained. The hydrogenated metal was then maintained in'the hydrogen atmosphere for twenty minutes at 850 C. and slowly cooled to 650 C. over a period of three hours and subsequently at a faster rate to room temperature. Examination of the microstructure of the hydrogenated product showed the presence of titanium hydride in clusters similar to the material illustrated in the figure.

The hydrogenated product was of good frangibility and could be crushed readily to fragments of a size less than maximum about one-half inch in a jaw crusher with production of minus 100 mesh fines only about 0.2%.

I claim: a I

1. A process for subdividing pieces of metal selected from the group consisting of alpha-beta and beta type titanium base alloys which comprises; hydrogenating said 4 pieces to provide therein a hydrogen content of between 0.5% and 2% by weight, heating said pieces at a temperature of'between 825 C. and 875 C. for a period of at least 15 minutes, slowly cooling said pieces to a temperature below 800 C. and subsequently crushing said pieces.

2. A process for subdividing pieces of metal selected from the group consisting of alpha-beta and beta type titanium base alloys which comprises; hydrogenating said pieces to provide therein a hydrogen content of between 0.5 and 2% by weight, heating said pieces at a temperature of between 825 C. and 875 C. for a period of at least 15 minutes, cooling said pieces at a rate not greater than 2 C. per minute to a temperature below 800 C. and subsequently crushing said pieces.

3. A process for subdividing pieces of metal selected from the group consisting of alpha-beta and beta type titanium base alloys which comprises; hydrogenating said pieces to provide therein a hydrogen content of between 0.5 and 2% by weight, heating said pieces at a temperature of between 825 C. and 875 C. for a period of at least 15 minutes, cooling said pieces at a rate not greater than 2 C. per minuteto a temperature below 650 C. and subsequently crushing said pieces.

4. A process for improving the firagibility of a hydrogenated titanium product of metal selected from the class of alpha-beta and beta type titanium base alloys which comprises; heating sa-id product at a temperature of from 825 C. to 875 C. for a period of at least 15 minutes and slowly cooling said product to a temperature below 800 C.

5. A process for improving the frangibility of a hydrogenated titanium product of metal selected from the class of alpha-beta and beta type titanium base alloys which comprises; heating said product at a temperature. of from 825 C. to 875 C. for a period of at least 15 minutes and slowly cooling said product to a temperature below 650 C.

6. A process for improving the frangibility of a hydrogenated titanium product of metal selected from the class of alpha-beta and beta type titanium base alloys which comprises; heating said product at a temperature of from 825 C. to 875 C. for a period of at least 15 minutes and cooling said product at a rate of not greater than 2 C. per minute to a temperature below 800 C.

References Cited in the file of this patent UNITED STATES PATENTS 7 Balke et a1. Feb. 8, 1938 OTHER REFERENCES ASM Preprint No. 98, 1958, pages 1 and 21; paper presented at the fortieth annual convention of the American Society for Metals, Cleveland, Ohio, Oct. 27 to 31, 1958. 

1. A PROCESS FOR SUBDIVIDING PIECES OF METAL SELECTED FROM THE GROUP CONSISTING OF ALPHA-BETA AND BETA TYPE TITANIUM BASE ALLOYS WHICH COMPRISES, HYDROGENATING SAID PIECES TO PROVIDE THEREIN A HYDROGEN CONTENT OF BETWEEN 0.5% AND 2% BY WEIGHT, HEATING SAID PIECES AT A TEMPERATURE OF BETWEEN 825*C. AND 875*C. FOR A PERIOD OF AT LEAST 15 MINUTES, SLOWLY COOLING SAID PIECES TO A TEMPERATURE BELOW 800*C. AND SUBSEQUENTLY CRUSHING SAID PIECES. 